The introduction of centrifugal force in HGMS field improves separation selectivity.The matrix rotation improves capture probability and recovery for magnetic particles.Centrifugal HGMS achieves an improved separation performance for fine ilmenite.Centrifugal HGMS presents a new method for separation of para-magnetic minerals.
High gradient magnetic separation (HGMS) has been an effective method for the concentration or removal of fine para-magnetic particles from suspension, but its powerful magnetic capture to magnetic particles results in the mechanical entrainment of non-magnetic particles in magnetic product, and thus reduces the separation selectivity. HGMS in centrifugal field (CHGMS) is proposed to improve the separation selectivity, and in this investigation a cyclic pilot-scale CHGMS separator was used to concentrate fine ilmenites from slurry. The theoretical descriptions on this CHGMS process indicate that the introduction of centrifugal field in the HGMS field has a promoting effect on the magnetic capture of matrix to magnetic particles and significantly improves the HGMS performance, and a minimum critical magnetic field force is required for the capture of magnetic particles in the centrifugal field. These theoretical descriptions were experimentally verified and the dependence of CHGMS performance on the key parameters such as centrifugal acceleration was determined. This CHGMS method has achieved a significantly improved separation selectivity and performance to the fine ilmenite, and thus provided a potential prospect in the development of CHGMS technology.
To recover heavy minerals from the Athabasca oil sands tailings, a roasting step is necessary to burn off the residual bitumen. However, most of the previous researchers, using a roasting step, did not seem to be able to separate the Fe-bearing titanium minerals (ilmenite and leucoxene) from the Fe-free titanium minerals (rutile and anatase). An investigation was therefore carried out to study the changes in magnetic properties after roasting to the types of minerals contained in the oil sands tailings. Ilmenite, hematite, and a rutile concentrate (LR Rutile) produced from the oil sands tailings (containing mainly leucoxene and rutile), were used in the study. It was observed that the magnetic susceptibility of ilmenite increased after either oxidation or reduction roasting at some intermediate temperatures and roasting time. For hematite, reduction roasting increased its magnetic susceptibility and oxidation roasting did not seem to have any effect. Reduction roasting of the LR Rutile resulted in an increase in its magnetic susceptibility, and this increase was mainly due to the contaminating Fe-bearing minerals (leucoxene). Upgrading of the LR Rutile was possible either by using low intensity magnetic separation following reduction roasting, or by using high intensity magnetic separation directly.
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To develop a flowsheet for separation of high grade titanium-rutile from ilmenite, that will meet market requirements. Rutile has a SGof 4.2, hardness 6.0 to 6.5 and is non-magnetic; while ilmenite has a SGof 4.5 to 5.0, hardness of 5.0 to 6.0, and is weakly magnetic. Both minerals are amenable to gravity concentration.
Titanium, the miracle metal, is a development resulting from the atomic and jet propulsion age. It is lighter than steel and stronger than aluminum, and has an almost unequaled resistance to corrosion. Titanium, a high-strength structural material has a corrosion- fatigue behavior in salt water, and exhibits complete immunity to many chemicals that pit and deteriorate most other metals. Its chief demands are as the metal in alloys, with a significant consumption as a white pigment in the paint industry. The value of titanium in sponge form is presently worth $9 to $10 a pound; in plate and sheet is 2 to 3X that.
The flowsheet shown was developed for a mixed rutile and ilmenite ore containing some magnetite. Concentration in this typical case starts at about 10 mesh and continues on into the minus 200 mesh fines. Gravity concentration starting as coarse as possible is very important in the recovery of a mixed ore of rutile and ilmenite, for a granular slime free product is muchmore amenable to subsequent magnetic and electrostatic separation. In any grinding circuit slimes are produced; if tonnage is considerable, flotation should be incorporated in flowsheet.
Conventional two stage open circuit crushing reduces the ore to about which is good feed to the rod mill. Sometimes a closed circuit reduction becomes necessary to ensure all minus or finer feed to the grinding circuit. Nature of the ore and its moisture content are factors considered in choosing circuit to be used.
crushed ore passes through a peripheral discharge Rod Mill at high dilution (35 to 40% solids). This minimizes over-grinding and sliming of the feed particles of titanium. The peripheral discharge product from the rod mill is elevated to a Duplex Mineral Jig making a rougher heavy mineral concentrate for retreatment in a Simplex Mineral Jig. The gravity flow through the jigs and Dillon Vibrating Screen returns the plus 20 mesh oversize to the rod mill for regrinding. This circuit recovers 40 to 50% of total titanium in a high grade granular product, ideal for magnetic and electrostatic separation.
The 20 mesh screen undersize is sized in a Hydraulic Classifier for most efficient tabling. Wilfley Tables with sand riffles handles the coarser sizes, while the finer sizes are handled on decks properly riffled for fine sands. This produces higher grade concentrates, maximum recovery and gives best table operation. Rougher table concentrates are cleaned on two separate tables, equipped as on the rougher table circuit. Cleaner table middlings are returned to the hydraulic classifier while the rougher table middlings go to the grinding circuit after being dewatered in a centrifugal cone, getting rid of the excess dilution. Gravity concentrates are flumed to a Dewatering Classifier. Hydraulic classifier overflow containing slimes and fines from the middling circuit overflowing the centrifugal classifier are thickened prior to waste or treatment by flotation.
Peripheral discharge Rod Mill receives crushed ore. Grinding under high dilution (35-40% solids) minimizes over grinding and sliming of fee particles of titanium. The fraction from the rod mill is elevated to a Duplex Mineral Jig.
The -10 micron slimes go to a thickener, purposely selected undersize to overflow the colloidal slimes, or through a Hydraulic Classifier to reject the colloids in the overflow. The deslimed cone underflow-density 65-70%goes to conditioner and flotation cells.
High density conditioning in a slightly acid circuit, pH 6.0 to 6.5, with H2SO4, sodium fluoride, and oleic acid actuates the titanium minerals for rapid flotation. This computation effectively rejects the gangue minerals and any apatite. Flotation is in Sub-A Flotation Machines with 30-35% solids with fuel oil and a frother added as necessary. The rougher concentrates are cleaned in an acidproof Sub-A Machine, by adding H2SO4 to lower pH to 5.0-5.5, which rejects gangue minerals and all phosphate minerals, to not more than a trace. Flotation cleaner middlings are recirculated to the rougher circuit for dilution.
Flotation concentrates are thickened and filtered; gravity concentrates are dewatered by a classifier, pan filter or internal drum filter. Concentrates are thoroughly dried, removing all surface coatings, and is done by conditioning the concentrates with chemicals to cut and wash off the surface film of soap and oils or blowing them off in a dryer.
Concentrates containing rutile, ilmenite, magnetite, zircon and possibly silica are sized over a vibrating screen and collected in separate storage hoppers ahead of dry processing, as each size is treated separately.
Low intensity magnetic separation pulls out metallic iron and magnetite. The concentrates pass through a high intensity magnetic separator to pull out the ilmenite fraction46 to 48% TiO2. The non-magnetic fraction is subjected to high intensity electrostatic separation which removes the high grade rutile94-95% TiO2. Rejects are treated by flotation to recover the zirconium.
Generally on complex titanium ores it is advisable to use the combination flowsheet shown. An ore of magnetite and ilmenite may, however, employ wet magnetic separation to remove magnetite, and all flotation for recovery of the ilmenite in a high grade product. In this case all the gravity circuit including the jigs and tables can be eliminated. This scheme is also applicable on a rutile ore with little or no ilmenite.Generally on complex titanium ores it is advisable to use the combination flowsheet shown. An ore of magnetite and ilmenite may, however, employ wet magnetic separation to remove magnetite, and all flotation for recovery of the ilmenite in a high grade product. In this case all the gravity circuit including the jigs and tables can be eliminated. This scheme is also applicable on a rutile ore with little or no ilmenite.
As the titanium industry rapidly develops, low-grade ilmenite resources are drawing global attention. The direct use of low-grade ilmenite can result in low production efficiency and heavy pollution. In addition, the production of high-titanium slag via electric furnace melting consumes significant energy and possesses low production efficiency. Therefore, a novel process with low energy consumption is necessary for producing ultra-grade slag (UGS) for chlorination. For low-grade ilmenite, semi-molten reduction and magnetic separation were suggested in this study. The effects of carbon content, reduction time, and Na2CO3 addition on the reduction and separation behavior were studied. The results showed that the addition of Na2CO3 favored the formation of a semi-molten state, which was more conducive for the diffusion, aggregation, and growth of the metal phase. In this regard, excess carbon was not helpful, and it weakened the growth of the metal phase. Wet grinding and magnetic separation were used for beneficiation of the reduced sample for efficiently separating the slag iron and preventing the formation of agglomerates between slag and metal. For the sample with a carbon dosage of 13 pct, Na2CO3 dosage of 8 pct, reduction temperature of 1673 K (1400C), and 90 minutes holding time, high-titanium slag with a TiO2 grade of 81.63 pct and iron content of 4.53 pct was produced, with the TiO2 recovery rate of 93.43 pct and the yields of 55.37 pct. High-titanium slag can be used as a high-quality raw material to produce UGS for chlorination by leaching.
Lv, X., Xin, Y., Lv, X. et al. High-Titanium Slag Preparation Process by Carbothermic Reduction of Ilmenite and Wet-Magnetic Separation. Metall Mater Trans B 52, 351362 (2021). https://doi.org/10.1007/s11663-020-02027-z
The effects of corrosion temperature, oxygen flow rate and corrosion time on the transformation of metallic iron were systematically studied, and the effects of mineral phases of Fe-bearing products on TiFe separation were investigated. The reaction mechanism of metallic iron in corrosion process was proposed. The results showed that corrosion temperature played a key role in determining the transformation of metallic iron in reduced ilmenite during corrosion process. Under suitable corrosion conditions, Fe-bearing mineral in reduced ilmenite could be converted to amorphous ferric hydroxide, lepidocrocite, hematite and magnetite, respectively, and lepidocrocite was the most easily separated Fe-bearing mineral from corrosion products owing to the significant density difference between lepidocrocite and Ti-rich materials. The Ti-rich material with 77.81 wt.% TiO2 and Fe-bearing product with 52.69 wt.% total Fe were obtained by gravity separation. The Ti recovery ratio and Fe recovery ratio were 91.16% and 86.27%, respectively.
The authors are grateful to the Natural Science Foundation of Hunan Province, China (Grant No. 2019JJ50816) and the National Natural Science Foundation of China (Grant No. 50504018) for supporting this research, and they acknowledge the support of State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization.
Zheng, Fq., Liu, X., Guo, Yf. et al. Transformation and separation of metallic iron in reduced ilmenite during corrosion process. J. Iron Steel Res. Int. 27, 13721381 (2020). https://doi.org/10.1007/s42243-020-00476-z